Techniques for addressing remote stations, such as repeaters in a communication system, are well known. In one such system, described in U.S. Pat. No. 3,410,968, a constant current power source, located at a terminal station, supplies operating power to the repeaters of a pair of oppositely propagating signal channels. Sections of the system can be isolated by the application at the terminal of voltage pulses to the power supply circuit. The first pulse induces a short circuit between the two channels at the first remote repeater station, thereby forming a loop-back path to the terminal. By the application of successive pulses, the short circuit is caused to move to successive stations. The effect is to isolate ever increasing portions of the two channels. The supply system voltage reading at the terminal station indicates at which remote station loop-back is occurring.
As is apparent, such a verification system requires a central power supply system for the repeaters and, hence, could not be used in a system wherein each repeater is powered by a local power supply.
In U.S. Pat. No. 3,172,965 each remote repeater is provided with a different frequency filter which uniquely characterizes the repeater. Thus, by measuring the frequency of a received signal it is possible to ascertain which of the repeaters is responding. This technique, however, requires that each repeater be different than every other repeater.
In contrast to the above examples, a preferred verification technique is one that can be used with all types of communication systems, and which permits the use of identical repeaters at all of the remote stations.